CVE-2019-13956
📋 TL;DR
CVE-2019-13956 is a remote code execution vulnerability in Discuz!ML multilingual forum software. Attackers can execute arbitrary PHP code by manipulating the language cookie parameter, potentially taking full control of affected systems. All Discuz!ML installations versions 3.2 through 3.4 are vulnerable.
💻 Affected Systems
- Discuz!ML
📦 What is this software?
Discuz\!ml by Codersclub
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, install backdoors, steal data, pivot to internal networks, and maintain persistent access.
Likely Case
Webshell deployment leading to data theft, defacement, or use as part of a botnet for further attacks.
If Mitigated
Limited impact if proper web application firewalls, input validation, and network segmentation are implemented.
🎯 Exploit Status
Exploitation is trivial with publicly available proof-of-concept code; attackers only need to modify a cookie value in HTTP requests.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 3.5 or later
Vendor Advisory: http://esoln.net/esoln/blog/2019/06/14/discuzml-v-3-x-code-injection-vulnerability/
Restart Required: No
Instructions:
1. Download Discuz!ML version 3.5 or later from the official source. 2. Backup your current installation and database. 3. Replace all files with the patched version. 4. Verify the language cookie handling is properly sanitized.
🔧 Temporary Workarounds
Web Application Firewall Rule
allBlock malicious language cookie patterns at the WAF level
Add WAF rule to detect and block cookie values containing PHP code patterns like '.phpinfo().' or suspicious characters
Input Validation Patch
allManually patch the vulnerable cookie handling code
Locate the language cookie processing code and add proper input validation/sanitization before use
🧯 If You Can't Patch
- Implement strict web application firewall rules to block malicious cookie patterns
- Isolate the vulnerable system in a segmented network with strict outbound traffic controls
🔍 How to Verify
Check if Vulnerable:
Test by sending a modified language cookie with PHP code (e.g., en'.phpinfo().') and checking if code executesCheck Version:
Check the Discuz!ML version in the admin panel or by examining the source code filesVerify Fix Applied:
After patching, repeat the test; code execution should be prevented and proper error handling should occur📡 Detection & Monitoring
Log Indicators:
- HTTP requests with language cookies containing PHP code patterns
- Unusual file creation/modification in web directories
- Webshell access patterns in access logs
Network Indicators:
- Outbound connections from web server to suspicious IPs
- Unusual HTTP POST requests with encoded payloads
SIEM Query:
web_access_logs WHERE cookie CONTAINS '.phpinfo().' OR cookie CONTAINS suspicious PHP functions